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Surface Science Studies of Metal Oxides Formed by Chemical Vapour Deposition on Silicon
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics I.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For an electronic device well-designed interfaces are critical for the performance. Studies of interfaces down to an atomic level are thus highly motivated both from a fundamental and technological point of view. In this thesis, a surface science approach has been employed to study the formation of interfaces in systems relevant for transistor and solar cell applications. Surface science methodology entails ultra high vacuum environment, single crystalline surfaces, submonolayer control of deposited material, surface sensitive spectroscopy and atomic resolution microscopy.

The primary experimental method for characterization is electron spectroscopy. This is a family of very powerful experimental techniques capable of giving information on the atomic level. Additionally, studies have been performed using scanning tunnelling microscopy. Combined these two methods can provide an atomic level characterisation of the geometric and electronic properties of the surface.

The emphasis of this work is placed on ultra thin TiO2 and ZrO2 films grown on silicon substrates by means of ultra-high vacuum metal-organic chemical vapour deposition. ZrO2 has also been grown on SiC and FeCrAl. Deposition has been performed with different process parameters. The interface region of each film has been characterised. The band alignment, a most important issue with regard to the development of new transistor devices, for the ZrO2/Si(100) system has been explored. Decomposition pathways of the metal organic precursors have been studied in detail. Changing process parameters is shown to alter both the precursor decomposition pathway and the nature of the interface region, thus opening the possibility to tailor the material function.

The titanium dioxide films grown in situ have shown to be excellent models of nanostructured electrode materials. In this spirit, interfaces of model systems for the solid-state dye-sensitized solar cell have been studied. Links between device performance and interface structure have been elucidated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2006. , p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 203
Keywords [en]
Physics, chemical vapour deposition, high-k, metal oxides, silicon, dye-solid interface, metal organic, electron spectroscopy, scanning tunnelling microscopy
Keywords [sv]
Fysik
Identifiers
URN: urn:nbn:se:uu:diva-7088ISBN: 91-554-6622-2 (print)OAI: oai:DiVA.org:uu-7088DiVA, id: diva2:168673
Public defence
2006-09-29, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2012-10-09Bibliographically approved
List of papers
1. Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation
Open this publication in new window or tab >>Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation
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2003 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 530, no 1-2, p. 63-70Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94705 (URN)10.1016/S0039-6028(03)00386-8 (DOI)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
2. UHV-MOCVD growth of TiO2 on SiOx/Si(111): Interfacial properties reflected in the Si 2p photoemission spectra
Open this publication in new window or tab >>UHV-MOCVD growth of TiO2 on SiOx/Si(111): Interfacial properties reflected in the Si 2p photoemission spectra
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2005 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 580, no 1-3, p. 207-217Article in journal (Refereed) Published
Abstract [en]

Metal–organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 °C and flux-limited growth at 500 °C. The interfacialproperties have been characterized by monitoring synchrotron radiation excited Si2pphotoemissionspectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiOx/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiOx/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO2)x(SiO2)y where x and y changes linearly and continuously over the interface. The model quantifies how (TiO2)x(SiO2)y mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94706 (URN)10.1016/j.susc.2005.02.016 (DOI)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
3. CVD of TiO2 on Si(111), SiOx/Si(111) and TiO2: Substrate and temperature dependence
Open this publication in new window or tab >>CVD of TiO2 on Si(111), SiOx/Si(111) and TiO2: Substrate and temperature dependence
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(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-94707 (URN)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2012-10-09Bibliographically approved
4. Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy
Open this publication in new window or tab >>Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy
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2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 4, p. 1008-1018Article in journal (Refereed) Published
Abstract [en]

The growth of ultrathin ZrO2 films on Si(1 0 0)-(2 × 1) and Si(1 1 1)-(7 × 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(1 1 1)-(7 × 7) the local structure of t-ZrO2 is not observed until a film thickness of 51 Å is reached. On Si(1 0 0)-(2 × 1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11 Å. The higher tendency for the formation of t-ZrO2 on Si(1 0 0) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(1 0 0), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(1 1 1) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.

Keywords
High dielectrics, Zirconium dioxide, Silicon, Chemical vapor deposition, Semiconductor–insulator interfaces, Synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94946 (URN)10.1016/j.susc.2006.11.038 (DOI)000245155800020 ()
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
5. Initial stages of ZrO2 chemical vapour deposition on Si(100)-(2x1) from zirconium tetra-tert-butoxide
Open this publication in new window or tab >>Initial stages of ZrO2 chemical vapour deposition on Si(100)-(2x1) from zirconium tetra-tert-butoxide
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-94709 (URN)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2012-10-09Bibliographically approved
6. Growth of ultrathin ZrO2 films on Si(100): Film-thickness dependent band alignment
Open this publication in new window or tab >>Growth of ultrathin ZrO2 films on Si(100): Film-thickness dependent band alignment
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2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 13, p. 132905-Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94710 (URN)10.1063/1.2190073 (DOI)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
7. Ultrathin ZrO2 films on Si-rich SiC(0 0 0 1)-(3 × 3): Growth and thermal stability
Open this publication in new window or tab >>Ultrathin ZrO2 films on Si-rich SiC(0 0 0 1)-(3 × 3): Growth and thermal stability
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2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 11, p. 2390-2400Article in journal (Refereed) Published
Abstract [en]

The growth and thermal stability of ultrathin ZrO2 films on the Si-rich Si(0001)-(3 x 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 degrees C yields tetragonal ZrO2. An interface is formed between the ZrO2 film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O-2. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO2 and ZrO2 occurs, possibly under the formation of silicate. The alignment of the ZrO2 and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 degrees C does not lead to decomposition of the tetragonal ZrO2 (t-ZrO2) but changes are observed within the interface region. After annealing to 1000 degrees C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO2 remnants, metallic Zr silicide and Si aggregates.

Keywords
zirconium dioxide; silicon carbide; chemical vapor deposition; semiconductor-insulator interfaces; synchrotron radiation photoelectron; spectroscopy; X-ray absorption spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94711 (URN)10.1016/j.susc.2007.04.026 (DOI)000247408600016 ()
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
8. Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy
Open this publication in new window or tab >>Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy
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2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 6, p. 875-879Article in journal (Refereed) Published
Abstract [en]

The initial stages of metal-organic chemical-vapor deposition of ZrO2 on a model FeCrAl alloy was investigated using synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy, scanning Auger microprobe, and time of flight secondary mass spectrometry. The coatings were grown in ultra-high vacuum at 400 degrees C and 800 degrees C using the single source precursor zirconium tetra-tert-butoxide. At 400 degrees C the coatings mainly consist of tetragonal ZrO2 and at 800 degrees C a mixed ZrO2/Al2O3 layer is formed. The Al metal diffuses from the FeCrAl bulk to the metal/coating interface at 400 degrees C and to the surface of the coating at 800 degrees C. The result indicates that the reaction mechanism of the growth process is different at the two investigated temperatures.

Keywords
metal-organic chemical-vapor deposition (MOCVD), zirconium tetra-tert-butoxide (ZTB), zirconium oxide, FeCrAl-alloy, time of flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94712 (URN)10.1016/j.tsf.2007.04.048 (DOI)000252980400001 ()
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
9. Surface chemistry of HfI4 on Si(100)-(2x1) studied by core level photoelectron spectroscopy
Open this publication in new window or tab >>Surface chemistry of HfI4 on Si(100)-(2x1) studied by core level photoelectron spectroscopy
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2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 4, p. 917-923Article in journal (Refereed) Published
Abstract [en]

The chemistry of HfI4 adsorbed on the Si(100)-(2 x 1) surface has been studied by core level photoelectron spectroscopy in ultra-high vacuum. Two stable surface intermediates are identified: HfI3 and HfI2, both of which remain upon heating to 690 K. The dissociation of HfI4 is accompanied by the formation of SiI. In addition, HfI4 is observed up to 300 K. Complete desorption of iodine occurs in the temperature regime 690-780 K. Deposition of HfI4 at 870 K results in a layer consisting of metallic Hf, whereas deposition at 1120 K results in the formation of Hf silicide. The results indicate that the metallic Hf formed at 870 K is in the form of particles. Oxidation of this film by O2 at low pressure does not result in complete Hf oxidation. This suggests that complete oxidation of Hf is a critical step when using HfI4 as precursor in atomic layer deposition.

Keywords
Atomic layer deposition, Chemisorption, Hafnium iodide, Hafnium oxide, Low index single crystal surfaces, Silicon, Synchrotron radiation photoelectron spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94713 (URN)10.1016/j.susc.2006.11.026 (DOI)000245155800008 ()
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14
10. Adsorption and Charge-Transfer Study of Bi-isonicotinic Acid on In Situ-Grown Anatase TiO2 Nanoparticles
Open this publication in new window or tab >>Adsorption and Charge-Transfer Study of Bi-isonicotinic Acid on In Situ-Grown Anatase TiO2 Nanoparticles
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2004 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 10, p. 3114-3122Article in journal (Refereed) Published
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-94714 (URN)10.1021/jp0344491 (DOI)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
11. Interfacial Properties of the Nanostructured Dye-Sensitized Solid Heterojunction TiO2/RuL2(NCS)2/CuI
Open this publication in new window or tab >>Interfacial Properties of the Nanostructured Dye-Sensitized Solid Heterojunction TiO2/RuL2(NCS)2/CuI
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2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 23, p. 11224-11232Article in journal (Refereed) Published
Abstract [en]

The interfaces of the nanostructured dye-sensitized solid heterojunction TiO2/Ru–dye/CuIhave been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO2 film sensitized with RuL2(NCS)2 [cis-bis(4,4-dicarboxy-2,2-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ(Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye–CuI interface and the changes brought upon the dye–TiO2 interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d–I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye–TiO2 bond breaking. Consequently, the very efficient charge injection channel provided by the dye–TiO2carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-94715 (URN)10.1063/1.1739399 (DOI)
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2017-12-14Bibliographically approved
12. Photovoltaic and Interfacial Properties of Heterojunctions Containing Dye-sensitized Dense TiO2 and Triarylamine derivatives
Open this publication in new window or tab >>Photovoltaic and Interfacial Properties of Heterojunctions Containing Dye-sensitized Dense TiO2 and Triarylamine derivatives
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2007 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 19, no 8, p. 2071-2078Article in journal (Refereed) Published
Abstract [en]

A series of solid-state heterojunctions comprising a dense TiO2 film electrode as an electron conductor, a ruthenium polypyridine complex (Ru(dcbpy)2(NCS)2) as a light-absorbing dye, and different triarylamine derivatives as hole conductors were prepared, and their photovoltaic properties as well as the molecular and electronic interfacial structures were investigated. The photovoltaic properties were compared to systems containing the hole conductors dissolved in an organic solvent as well as to a system containing a liquid electrolyte containing the iodide/tri-iodide redox couple. Two of the solid-state heterojunctions showed conversion efficiencies close to those of the system containing the iodide/tri-iodide redox couple, while one system was clearly less efficient. To explain the differences in photovoltaic properties the electronic and molecular interfacial structures of the solid-state heterojunctions were investigated by photoelectron spectroscopy (PES). By valence level PES the electronic energy levels highest in energy for the dye and the hole conductors were mapped, and the differences in energy matching partly explain the trends in photovoltaic properties. Differences in the molecular surface structure of the heterojunctions were also observed from the N Is core level measurements. Specifically it was found that the smaller hole conductor, showing low photocurrent yield, is inserted into the dye layer.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-94531 (URN)10.1021/cm062498v (DOI)000245549500028 ()
Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2017-12-14Bibliographically approved

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